Influenza viruses for use in preparing human vaccines have traditionally been grown on embryonated hen eggs, although more modern techniques grow the virus in mammalian cell culture e.g. on Vero cells, MDCK cells or PER.C6 cells. The change in virus growth substrate has provided an opportunity for regulatory re-assessment of influenza vaccine safety. For example, contamination with host cell DNA has been a regulatory concern for the cell-derived vaccines [1], but has not been of concern in the past for vaccines grown in eggs.
The safety issues surrounding egg-derived influenza vaccines are thus different from those surrounding vaccines grown in cell culture, with cell-derived vaccines being under closer scrutiny. It is an object of the invention to address these different safety issues, and in particular to provide methods for enhancing the safety of influenza vaccines grown on cell culture.